1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to efficiently retransmitting data in a wireless network environment.
2. Description of the Related Art
With the advent of the ubiquitous computing and recent developments in network technology, research has been conducted regarding wireless network techniques that are region independent and convenient. Wireless networks are advantageous in terms of transmitting data without using lines. However, in wireless networks, a plurality of devices must share limited wireless resources to transmit considerable amounts of multimedia data. Thus, the more severe the contention for wireless data resources becomes, the more likely that wireless data resource loss wireless data loss will occur. In this regard, wireless networks are less efficient than wired networks. In order to safely transmit data and reduce data loss and collisions between data transmissions conducted in a wireless network environment, a distributed coordination function (DCF) and a point coordination function (PCF) have been widely used. In particular, in a wireless personal area network (PAN) environment, a channel time allocation method can be used.
The aforementioned problem with wireless networks can be addressed by using a DCF, a PCF, or a channel time allocation method. However, there still remains other problems associated with the inherent characteristics of wireless networks such as multi-paths, fading, and interference, and these are obstacles to the smooth transmission of data. As the number of wireless networks increases, data loss and collisions between data transmissions are more likely to occur, and the frequency of data retransmissions that adversely affect the speed of transmission of data in a wireless network is more likely to increase. This is especially the case for such data as audio/video (A/V) data that needs to be precisely transmitted and thus requires a high quality of service (QoS). Thus, improved data retransmission methods capable of securing as wide an available bandwidth as possible by reducing the number of data retransmissions are needed.
FIG. 1 is a diagram for explaining a related art method of transmitting data between related art wireless devices. Referring to FIG. 1, in a wireless network environment, a transmitting device generates a plurality of headers for a media access control (MAC) layer (MAC HDR) and a physical (PHY) layer (PHY HDR), i.e., a MAC header and a PHY header respectively, and transmits information consisting of the PHY header, the MAC header, and data 1 to a receiving device according to the IEEE 802.11 standard. Then, the receiving device precisely receives the first data frame a short inter frame space (SIFS) after the transmission of the first data frame by the transmitting device according to the IEEE 802.11 standard. If no error is detected from the first data frame, the receiving device transmits the first data frame to an upper layer, and transmits an acknowledgement (ACK) frame consisting of a PHY header, an MAC header, and ACK 1 to the transmitting device in order to notify the transmitting device that the first data frame has been successfully received by the receiving device 2000. The transmitting device receives the ACK frame transmitted by the receiving device, and transmits a second data frame consisting of a PHY header, an MAC header, and data 2 to the receiving device a DCF inter frame space (DIFS) after the reception of the ACK frame, according to the IEEE 802.11 standard.
FIG. 2 is a diagram for explaining a related art method of handling a failure or error in the transmission of data between wireless devices. Referring to FIG. 2, a transmitting device transmits data 1 to a receiving device. If data 1 is smoothly transmitted to the receiving device, the receiving device transmits ACK 1 to the transmitting device, and transmits data 1 to an upper layer. The transmitting device receives ACK 1, and then transmits data 2 to the receiving device. As soon as the transmitting device transmits data 2 to the receiving device, a counter begins to operate. If the counter stops operating and an acknowledgement is not received from the receiving device within an acknowledgement timeout period (ACK Timeout) after the transmission of data 1, the transmitting device determines that the transmission of data 2 has failed, and retransmits data 2 to the receiving device. In this case, the receiving device abandons data 2 instead of transmitting it to an upper layer. The transmitting device can retransmit data 2 to the receiving device a number of times, corresponding to a retry limit value. If the transmitting device receives no acknowledgement from the receiving device even though the transmitting device has retransmitted data 2 to the receiving device as many times as indicated by the retry limit value, the transmitting device skips data 2, and transmits data 3 to the receiving device. If data is received by the receiving device and an error is not detected from data 3, the receiving device transmits data 3 to the upper layer, and transmits ACK 3 to the transmitting device.
In the related art, a transmitting device must transmit data to a receiving device in units of frames and receive an ACK frame from the receiving device for each frame transmitted by the transmitting device, thereby wasting time sequentially transmitting a plurality of frames. Also, the transmission of data between the transmitting device and the receiving device may not be smooth, as in the case of transmission of data 2 illustrated in FIG. 2. In addition, an MAC header and a PHY header are attached to each frame, thereby limiting the amount of data that can be transmitted at a time and reducing the efficiency of data transmission. Moreover, the transmission of short frames such as A/V stream data frames may result in relatively high overheads.